AP lumbar spine X-ray positioning
One of the routine L-spine views. The patient lies on their back, the beam passes front to back (AP), straight on to the receptor, and the centring point is L3, at the lower costal margin.
By the ScanFlo Editorial Team · Updated
In this section · X-ray positioning
- X-ray positioning guides
- Skull positioning
- Face & sinuses positioning
- Soft tissue neck positioning
- C-spine positioning
- Chest positioning
- Shoulder positioning
- Humerus positioning
- Elbow positioning
- Forearm positioning
- Wrist positioning
- Hand positioning
- T-spine positioning
- Abdomen positioning
- L-spine positioning
- Sacrum & SI joints positioning
- Pelvis positioning
- Hip positioning
- Femur positioning
- Knee positioning
- Tibia & fibula positioning
- Ankle positioning
- Foot positioning
Still being checked: a radiographer is reviewing this guide. If your department does it differently, follow your department.
Patient position
Supine. Supine with the knees bent so the lower back lies flat on the table. For trauma, leave the patient lying as found and take the AP or PA from that position.
Centring & collimation
Central ray
APCentre: L3, at the lower costal margin.
Beam: AP, perpendicular to the receptor.
Collimate: T12 to the sacrum, including the sacroiliac joints
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | |
| Receptor | 18 × 43 cm | portrait |
| Placement | Table bucky | Grid in |
| Angulation | None | Perpendicular to the receptor |
Marker & breathing
- Marker: anatomical side marker on the side being examined, clear of anatomy
- Breathing: Breathe out and hold.
Exposure by patient size
Treat these as a starting point. Your detector, your generator and the patient in front of you will all move the numbers.
| Patient size | kV | mAs (chart) | mAs (DR default) |
|---|---|---|---|
| XS | 70 | 12.5 | 16 |
| S | 70 | 20 | 25 |
| M | 70 | 25 | 32 |
| L | 70 | 40 | 50 |
These start from a classic film-screen chart (70 kV, 50 mAs at 140 cm) and are adjusted for a digital detector at 100 cm. The DR column is what ScanFlo's console suggests; each step up or down changes the mAs by about a quarter.
Image quality checklist
- T12 to the sacrum and the sacroiliac joints shown.
- Spinous processes central; intervertebral spaces open.
- The anatomical side marker is visible, correct and clear of the anatomy.
- Collimation borders are visible on all sides, no wider than the area requested.
Faults & how to fix them
| Fault | Cause | Fix |
|---|---|---|
| Spaces closed | Lumbar lordosis | Flex the knees to flatten the back. |
Common questions
- Where do you centre for a lumbar spine AP X-ray?
- The centring point is L3, at the lower costal margin.
- What distance and beam angle does a lumbar spine AP need?
- 100 cm from the tube to the receptor. The beam passes front to back (AP), straight on to the receptor.
- What size receptor, and do you need a grid?
- Use an 18 × 43 cm receptor, portrait, in the table bucky. A grid is needed.
- What should the patient do with their breathing?
- Ask them to breathe out and hold it while you expose.
- What goes wrong most often on a lumbar spine AP?
- Spaces closed. Usual cause: lumbar lordosis. The fix: flex the knees to flatten the back.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a lumbar spine ap in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.